1. Field of the Invention
The present invention relates to a gallium nitride-based compound semiconductor chip produced by growing a gallium nitride-based compound semiconductor crystal on a gallium nitride substrate with a wurtzite type crystal structure and dividing the resulting wafer, a method for producing such a chip, and a gallium nitride-based compound semiconductor wafer.
2. Description of the Related Art
A light emitting device using a gallium nitride-based compound semiconductor is capable of emitting light with wavelengths widely ranging from blue to orange by adjusting a composition of each of the compound semiconductor layers therein. Such gallium nitride-based compound semiconductor light emitting devices have been conventionally produced by growing a gallium nitride-based compound semiconductor film on a sapphire substrate, the crystal structure of which is a rhombohedral structure, by using a metal organic chemical vapor deposition method or the like. However, a gallium nitride-based compound semiconductor crystal formed on a sapphire substrate is poor in quality because a lattice incommensurate between the sapphire substrate and the gallium nitride-based compound semiconductor crystal is significant. Therefore, a high light emission efficiency cannot be achieved. This is why attempts are being made to produce a light emitting device by producing a gallium nitride substrate and growing a gallium nitride-based compound semiconductor thereupon. However, the gallium nitride substrate has a crystal structure which is a wurtzite type structure, unlike the sapphire substrate which has a rhombohedral structure. No methods have been devised for producing a wafer by growing the gallium nitride-based compound semiconductor crystal on the gallium nitride substrate having the wurtzite type structure and forming an electrode thereon, and dividing the wafer into chips.
In a wafer produced by growing a gallium nitride-based compound semiconductor crystal on a gallium nitride substrate having a wurtzite type structure, there is no lattice incommensurate between the gallium nitride substrate and the gallium nitride-based compound semiconductor crystal. Therefore, the quality of the gallium nitride-based compound semiconductor crystal in such a wafer is satisfactory. However, with regard to producing a wafer by growing a gallium nitride-based compound semiconductor crystal on a gallium nitride substrate having a wurtzite type crystal structure and forming an electrode thereon, and dividing the wafer into gallium nitride-based compound semiconductor chips are light emitting devices, no reports have been made in relation to the following: (1) what an approximate thickness of the wafer should be and what a division facet direction of the wafer should be in order to produce satisfactory chips with no defects in the shape, such as nicks or the like; (2) how grooves for assisting chip division should be formed; and (3) how the chip division should be made.
The inventors of the present invention examined a technique in the chip division of a wafer produced by growing a gallium nitride-based compound semiconductor crystal on a gallium nitride substrate having a (0001) facet of a wurtzite type crystal structure as a principal facet. Such a technique has never been put into practice. A method has been found for producing a gallium nitride-based compound semiconductor chip as a light emitting device of a satisfactory shape without nicks or the like at a high yield, and the structure of the gallium nitride-based compound semiconductor chip also has been disclosed.
A nitride semiconductor light emitting chip is a gallium nitride-based compound semiconductor chip including a gallium nitride substrate with a (0001) facet of a wurtzite type crystal structure as a principal facet, and a gallium nitride-based compound semiconductor crystal grown on the gallium nitride substrate. The gallium nitride-based compound semiconductor chip is characterized in that at least one of the division facets thereof is a cleave facet of the gallium nitride substrate.
Cleave facets of the wurtzite type crystal in directions can be deviated by 60 degrees from one another. Division is relatively easy in the cleave facet direction, while division is difficult in a direction substantially perpendicular to the cleave facet. The ease of division in such a substantially perpendicular direction is different from that in the cleave facet direction, thereby causing defects in the shape of the chips, such as nicks or the like. The present invention decreases the number of defects in the shape of the chips, such as nicks or the like. Therefore, chips having satisfactory cross-sectional portions can be produced at a high yield.
The thickness of the gallium nitride substrate may be in the range between 50 xcexcm or more and 250 xcexcm or less. When the thickness of the gallium nitride-substrate is greater than 250 xcexcm, the number of the chips having defects in the shape, such as nicks or the like, increases in the chip division step because the gallium nitride substrate is relatively hard. When the thickness of the wafer is smaller than 50 xcexcm, the wafer becomes easy to break in wafer polishing and chip division steps. When the thickness of the gallium nitride substrate is in the range between 50 xcexcm or more and 250 xcexcm or less, the number of defects in the shape of the chips, such as nicks or the like, is few and the wafer substantially does not break in the polishing and chip division steps.
The nitride semiconductor light emitting chip of the present invention is characterized by having a structure such that at least one of the chip division facets is a facet substantially perpendicular to a cleave facet of the gallium nitride substrate.
According to the present invention, it is possible to prevent production yield in the chip division step from decreasing because an adjustment in direction of the grooves is made with ease and the deviations in the direction are minimized by forming the chip division facet in a direction substantially perpendicular to the cleave facet. Moreover, the grooves are formed in a direction substantially perpendicular to the cleave facet so that an angle of the chip does not become acute, thereby substantially eliminating the occurrence of nicks in a chip.
The nitride semiconductor light emitting chip of the present invention is characterized by having a structure such that the side length of the division facet in the cleave facet direction of the gallium nitride substrate is longer than that in the division facet substantially perpendicular to the cleave facet of the gallium nitride substrate.
According to the present invention, it is possible to produce a rectangular chip such that a shorter side direction thereof is a direction substantially perpendicular to a cleave facet direction and a longer side direction thereof is a cleave facet direction. A greater force is applied to the shorter side, since division is not easily made in the direction perpendicular to the cleave facet direction. Therefore, an appropriate force can be applied to a groove based on leverage so that the chips are produced at a high yield.
The nitride semiconductor light emitting chip of the present invention is characterized by having a structure such that all of the chip division facets are the cleave facets of the gallium nitride substrate. Because of this characteristic, the number of defects in the shape of the chips, such as nicks or the like, may be few. Accordingly, a chip having a satisfactory condition of the cross-sectional portions can be produced at a high yield.
The gallium nitride-based compound semiconductor chip of the present invention includes a gallium nitride substrate with a (0001) facet of a wurtzite type crystal structure as a principal facet and a gallium nitride-based compound semiconductor crystal formed on the gallium nitride substrate. The gallium nitride-based compound semiconductor chip is characterized in that at least two of the chip division facets deviate by 15 degrees from the cleave facet of the gallium nitride substrate and are formed in directions substantially perpendicular to each other. When the division facets are formed in the directions deviated by 15 degrees from the cleave facet, that is, at least two of the division facets deviate by 15 degrees from the cleave facet. Therefore, the division in one facet is not easier than that in the other facet, such that, the ease of division is equal in both directions or the difference in the ease of division becomes less. Therefore, the division is equally made in both facets and the number of defects in the shape of the chips, such as nicks or the like, may be few.
The thickness of the gallium nitride substrate may be in the range between 50 xcexcm or more and 250 xcexcm or less. When the thickness of the gallium nitride-substrate is greater than 250 xcexcm, the number of the chips having defects in the shape, such as nicks or the like, increases in the chip division step because the gallium nitride substrate is relatively hard. When the thickness of the wafer is smaller than 50 xcexcm, the wafer becomes easy to break in the wafer polishing and chip division steps. When the thickness of the gallium nitride substrate is in the range between 50 xcexcm or more and 250 xcexcm or less, the number of defects in the shape of the chips, such as nicks or the like, is few and the wafer substantially does not break in the polishing and chip division steps.
A method for producing a gallium nitride-based compound semiconductor chip of the present invention is characterized by including: a wafer formation step of forming a wafer having a gallium nitride-based compound semiconductor crystal grown on a gallium nitride substrate with a (0001) facet of a wurtzite type crystal structure as a principal facet so that the thickness of the gallium nitride substrate is in the range between 50 xcexcm or more and 250 xcexcm or less; a groove formation step of forming grooves for the chip division on the wafer; and a division step of dividing the wafer into gallium nitride-based compound semiconductor chips.
The gallium nitride substrate with a (0001) facet of a wurtzite type crystal structure as a principal facet is formed so as to have the thickness in the range between 50 xcexcm or more and 250 xcexcm or less. Therefore, the number of defects in the shape of the chips, such as nicks or the like, is few and the wafer does not break in the polishing and chip division steps.
The present invention is characterized in that the groove formation step includes a step of forming grooves in a cleave facet direction of the gallium nitride substrate and a step of forming grooves in a direction substantially perpendicular to the cleave facet direction.
According to the present invention, it is possible to prevent production yield in the chip division step from decreasing because an adjustment in the direction of the grooves is made with ease and the deviations in the direction are minimized by forming the chip division facet in directions substantially perpendicular to each other. Moreover, the grooves are formed in a direction substantially perpendicular to the cleave facet so that an angle of the chip does not become acute, thereby substantially eliminating the occurrence of nicks in a chip.
The present invention is characterized in that the groove formation step includes a step of forming grooves in directions substantially perpendicular to each other, and each direction deviates by 15 degrees from the cleave facet of the gallium nitride substrate.
According to the present invention, the grooves are formed in mutually orthogonal directions deviated by 15 degrees from the cleave facet. The wafer is divided along the grooves formed in such directions so that the division facets are formed in the directions deviated by 15 degrees from the cleave facet. Therefore, both of the facets equally deviate from the cleave facet and division in one facet cannot be easier than that in another facet. Since the ease of division is equal in both directions of the difference in the ease of division becomes less, the division is equally made in both facets and the number of defects in the shape of the chips, such as nicks or the like, may be few.
The groove formation step may include a step of forming grooves on both sides of the wafer so that the grooves on one side are formed in positions corresponding to the grooves on the other side. Therefore, the ease of the chip division is improved and a production yield of the chips of satisfactory quality may be further improved.
A method for producing a gallium nitride-based compound semiconductor chip of the present invention is characterized by including: a wafer formation step of forming a wafer having a gallium nitride-based compound semiconductor crystal grown on a gallium nitride substrate with a (0001) facet of a wurtzite type crystal structure as a principal facet; a groove formation step of forming grooves in a cleave facet direction of the gallium nitride substrate; and a division step of dividing the wafer into gallium nitride-based compound semiconductor chips.
According to the present invention, the number of defects in the shape of the chips, such as nicks or the like, may be few because of the chip division made in a cleave facet of the wurtzite type crystal structure. Accordingly, chips having a satisfactory condition of the cross-sectional portions can be produced at a high yield.
A method for producing a gallium nitride-based compound semiconductor chip of the present invention is characterized in that the wafer formation step includes a step of producing the wafer so that the thickness of the gallium nitride substrate is in the range between 50 xcexcm or more and 250 xcexcm or less.
When the thickness of the gallium nitride-substrate is greater than 250 xcexcm, the number of the chips having defects in the shape, such as nicks or the like, increases in the chip division step because the gallium nitride substrate is relatively hard. When the thickness of the wafer is smaller than 50 xcexcm, the wafer becomes easy to break in the wafer polishing and chip division steps. When the thickness of the gallium nitride substrate is in the range between 50 xcexcm or more and 250 xcexcm or less, the number of defects in the shape of the chips, such as nicks or the like, is few and the wafer substantially does not break in the polishing and chip division steps.
A method for producing a gallium nitride-based compound semiconductor chip of the present invention is characterized in that the groove formation step includes a step of forming grooves in a direction substantially perpendicular to the cleave facet direction of the gallium nitride substrate.
According to the present invention, it is possible to prevent a production yield in the chip division step from decreasing because an adjustment in the direction of the grooves is made with ease and the deviations in the direction are minimized by forming the chip division facet in a direction substantially perpendicular to the cleave facet. Moreover, the grooves are formed in a direction substantially perpendicular to the cleave facet so that an angle of the chip does not become acute, thereby substantially eliminating the occurrence of nicks in a chip.
A method for producing a gallium nitride-based compound semiconductor chip is characterized in that the groove formation step includes a step of forming grooves so that the length of the grooves corresponding to a single chip formed in the cleave direction of the gallium nitride substrate is longer than the length of the grooves corresponding to a single chip formed in a direction substantially perpendicular to the cleave facet direction of the gallium nitride substrate.
According to the present invention, it is possible to produce a rectangular chip such that a shorter side direction thereof is a direction substantially perpendicular to a cleave facet direction and a longer side direction thereof is a cleave facet direction. A greater force is applied to the shorter side, since division is not easily made in the direction perpendicular to the cleave facet direction. Therefore, an appropriate force can be applied to a groove based on leverage so that the chips are produced at a high yield.
A method for producing a gallium nitride-based compound semiconductor chip of the present invention is characterized in that the groove formation step includes a step of forming grooves along at least two cleave facet directions of the gallium nitride substrate so that the grooves substantially surround certain regions on the wafer.
Because of this characteristic, all of the division facets may be the cleave facets of the gallium nitride substrate. Therefore, the number of defects in the shape of the chips, such as nicks or the like, may be few. Accordingly, a chip having a satisfactory condition of the cross-sectional portions can be produced at a high yield.
A method for producing a gallium nitride-based compound semiconductor chip of the present invention is characterized by including: a wafer formation step of forming a wafer having a gallium nitride-based compound semiconductor crystal grown on a gallium nitride substrate with a (0001) facet of a wurtzite type crystal structure as a principal facet; a groove formation step of forming grooves in directions substantially perpendicular to each other, each of the directions of grooves deviates by 15 degrees from the cleave facet of the gallium nitride substrate; and a division step of dividing the wafer into gallium nitride-based compound semiconductor chips.
When the division facets are formed in the directions deviated by 15 degrees from the cleave facet, that is, at least two of the division facets deviate by 15 degrees from the cleave facet. Therefore, the division in one facet is not easier than that in the other facet, such that, the ease of division is equal in both directions or the difference in the ease of division becomes less. Therefore, the division is equally made in both facets and the number of defects in the shape of the chips, such as nicks or the like, may be few.
The gallium nitride-based compound semiconductor wafer of the present invention includes a gallium nitride substrate with a (0001) facet of a wurtzite type crystal structure as a principal facet and a gallium nitride-based compound semiconductor crystal grown on the gallium nitride substrate. The grooves are formed on a surface of the gallium nitride-based compound semiconductor wafer at least in a cleave facet direction of the gallium nitride substrate.
The wafer of the present invention is divided relatively easy in a cleave facet of the wurtzite type crystal structure, thereby decreasing the number of defects in the shape of the chips, such as nicks or the like. Therefore, chips having a satisfactory condition of the cross-sectional portions can be produced at a high yield by dividing the wafer.
Grooves are formed on the surface of the gallium nitride-based compound semiconductor wafer in a direction substantially perpendicular to the cleave facet direction of the gallium nitride substrate.
According to the present invention, it is possible to prevent production yield in the chip division step from decreasing because an adjustment in direction of the grooves is made with ease and the deviations in the direction are minimized by forming grooves on the surface of the gallium nitride-based compound semiconductor wafer in a direction substantially perpendicular to the cleave facet direction. Moreover, the grooves are formed in a direction substantially perpendicular to the cleave facet so that an angle of the chip does not become acute, thereby substantially eliminating the occurrence of nicks in a chip.
The gallium nitride-based compound semiconductor wafer of the present invention is produced so that a depth of the grooves substantially perpendicular to the cleave facet direction of the gallium nitride substrate is greater than a depth of the grooves in the cleave facet direction of the gallium nitride substrate. The ease of division is equal in both directions or the difference in the ease of division becomes smaller, thereby producing chips of satisfactory quality without defects, such as nicks or the like.
The gallium nitride-based compound semiconductor wafer of the present invention is produced so that the grooves are formed on the gallium nitride-based compound semiconductor crystal. Therefore, it is possible to improve an yield of chip division because the accuracy of the position adjustment of the grooves improves and thus deviation in the position of the grooves is reduced.
The gallium nitride-based compound semiconductor wafer of the present invention is characterized in that all of the grooves are formed in the cleave facet direction of the gallium nitride substrate. All of the division facets of the gallium nitride-based compound semiconductor chips can be cleave facets of the gallium nitride substrate. Therefore, it is possible to produce chips having a satisfactory shape at a high yield.
The gallium nitride-based compound semiconductor wafer of the present invention is characterized in that grooves are formed on one surface and further grooves are formed on a surface opposite from said one surface so as to correspond to the grooves formed thereon. Therefore, the ease of the chip division can be improved and production yield of satisfactory chips can be further improved.
The gallium nitride-based compound semiconductor wafer of the present invention comprises a gallium nitride substrate with a (0001) facet of a wurtzite type crystal structure as a principal facet and a gallium nitride-based compound semiconductor crystal formed on the gallium nitride substrate. Grooves are formed on a surface of the gallium nitride-based compound semiconductor wafer in directions substantially perpendicular to each other so that each of the directions of the grooves deviates by 15 degrees from a cleave facet direction of the gallium nitride substrate.
According to the present invention, when the grooves on a surface of the wafer are formed in mutually orthogonal directions deviated by 15 degrees from the cleave facet, both of the facets on the surface of the wafer deviate by 15 degrees from the cleave facet. Therefore, the division in one facet is not easier than that in another facet. Therefore, the division is equally made in both facets and defects in the shape of the chips, such as nicks or the like, substantially does not occur.
In a method for forming chip division grooves, a scriber or dicer or etching technique may be used. In the case of using a wet etching technique, for example, a mixed acid of sulfuric acid and phosphoric acid can be used. In the case of using a dry etching technique, a method such as reactive ion etching, ion milling, focused ion beam etching, ECR etching, etc., can be used.
Thus, the invention described herein makes possible the advantages of: (1) providing a gallium nitride-based compound semiconductor chip having a satisfactory shape produced as a result of dividing a wafer using a gallium nitride substrate having a wurtzite type crystal structure; (2) providing a method for producing such a chip at a high yield; and (3) providing a gallium nitride-based compound semiconductor wafer divided into chips having a satisfactory shape.